sem_post - unlock a semaphore
#include <semaphore.h>
int sem_post(sem_t *sem);
Link with -pthread.
sem_post() increments (unlocks) the semaphore pointed to by sem. If the semaphore's value consequently becomes greater than zero, then another process or thread blocked in a sem_wait(3) call will be woken up and proceed to lock the semaphore.
sem_post() returns 0 on success; on error, the value of the semaphore is left unchanged, -1 is returned, and errno is set to indicate the error.
- EINVAL
- sem is not a valid semaphore.
- EOVERFLOW
- The maximum allowable value for a semaphore would be exceeded.
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
| sem_post () | Thread safety | MT-Safe |
sem_post() is async-signal-safe: it may be safely called within a signal handler.